Beam deflection system comprising a flattened helix



April 2, 1968 c, Low ETAL 3,376,464

BEAM DEFLECTION SYSTEM COMPRISING A FLATTENED HEL Filed NOV. 21, 1966 2Sheets-Sheet 1 INVENTORS CHARLES LOTY ANDRE EUGENE GUILLAUME, DECEASEDGEORGES ALBERT BOUTRY, R PRESENTATIVE BY 2M AGENT April 2, 1968 c. LOTYETAL BEAM DEFLECTION SYSTEM COMPRISING A FLATTENED HELIX 2 Sheets-Sheet2 Filed Nov. 21, 1966 FIG.3

INVENTORS CHARLES LOTY EUGENE GUILLAUME DECEASED GEORGES ALBERT BOU TRY,RE E ANDRE RESENTATIVE AGENT United States Patent 3,376,464 BEAMDEFLECTION SYSTEM COMPRISING A FLATTENED HELIX Charles Loty,Nogent-sur-Marne, France, and Andr Eugene Guillaume, deceased, late ofCrosne, France, by Georges-Albert Boutry, representative, Viilencresnes,France, assignors to Laboratoires dElectronique et tle PhysiqueAppiiquees LE1.

Filed Nov. 21, 1966, Ser. No. 596,011 Claims priority, applicationFrance, Nov. 30, 1965, 40 19' 3 5 Ciaims. for. 3115-4 ABSCT 0F THEDISCLOSURE The invention relates to a charged particle beam deflectionapparatus, consisting of a system of two electrodes, one of which is ahelical Winding of substantially flat conductive ribbon, having aflattened part parallel to the axis of the winding.

The invention is particularly, though not exclusively, related to acathode-ray tube, comprising an electron gun for the production of anelectron beam and comprising a charged particle beam deflectionapparatus of the above kind for the deflection of the electron beam.

As an apparatus for the deflection of a charged particle beam 21 systemhas been widely used consisting of two electrodes placed at oppositesides of the path of the beam. A large number of the existingcathode-ray tubes is provided with one or more of such systems for thedeflection of the electron beam. However, these systems involve an upperlimit for the frequencies of the voltage signals which may yield anadequate deflection of the charged particle beam. When the time oftransit of the charged particles through the deflection region becomescomparable with the period of the deflecting signals, there an adequatedeflection is not obtained.

In order to make these apparatus appropriate for a broad band-width ithas been proposed to construct the system consisting of the twoelectrodes in the form of a transmission line. An electromagnetic wavepropagating along a transmission line and influencing a charged particlebeam propagating in its immediate neighborhood can give an adequatedeflection of the beam, when the velocities of the wave and of the beamare substantially equal. This situation can easily be obtained. Thetransmission line may reduce the apparent velocity of the electromagnetic wave to a fraction of its velocity of propagation in themedium, for instance to a tenth of it, and the velocity of the chargedparticle beam may be fitted by means of a convenient electric field.

3,376,464 Patented Apr. 2, 1968 It is, of course, very important, thatin a deflection apparatus consisting of a system of two electrodes,which form a transmission line, the signals are not deformed duringpropagation along the transmission line. The principal causes ofdistortion are the time of transit through the transmission line, theattenuation and the dispersion of the phase velocities. The mostimportant cause of distortion is the dispersion of the phase velocities.In order to reduce this the mode of propagation called T.E.M. is used,wherein the wave has transverse electric and magnetic fields andpropagates along the electrodes with a velocity independent of thefrequency and equal to the velocity of light. As the charged particlebeam has a much smaller velocity, it is necessary to have a line with along length and to wind it in order to obtain the required retardation.

Until now the most promising constructions of a system, wherein the twoelectrodes, between which the voltage differences for the deflection ofthe beam are applied, form a transmission line, seem to be theconstructions, wherein one of these electrodes is constructed in theform of a helical winding of substantially flat conductive ribbon,having a flattened part parallel to the axis of the winding. At present,there are a number of known different deflection apparatus constructedin this manner.

In some of these apparatus the second electrode of the deflection systemis disposed Within the helical winding. There is known, for instance, atype, wherein the second electrode is a stainless steel arbor surroundedby a ceramic spacer around which the helical winding is wound. Thestainless steel arbor has a flattened part parallel to its axis, andparallel to the flattened part of the helical winding. The ceramicspacer has an opening between these flattened parts of the electrodes.The charged particle beam passes through this opening, which isrectangular in cross-section.

In others of these apparatus, the helical winding is disposed within thesecond electrode of the deflection system. There are known, forinstance, types, wherein the second electrode is a hollow cylinder,flattened along one side and wherein the helical winding is wound on aninsulating former contained within the second deflection electrode theinsulating former being of such shape and so positioned, that thehelical winding has a flattened region parallel to, immediately oppositefrom the flattened regions of the second electrode. The flattenedregions of the electrodes lie on opposite sides of the char ed particlebeam path and extend along it.

There are also known some of these apparatus, wherein each of the twoelectrodes is a helical winding. The two helical windings are hereinplaced on opposite sides of the path of the charged particle beam in asymmetrical manner. There is, for instance, known a type, wherein eachof the two helical windings is disposed about a grounded planarconductive sheet. Each winding is wound close to the grounded plane in aflat oval fashion.

The known apparatus indicated above can give an adequate deflection ofthe beam for signals of a fairly high frequency. Yet, these apparatuspermit the existence of a dispersion of the phase velocities whichcannot be neglected.

It is an object of the invention, to provide a charged particle beamdeflection apparatus wherein the two deflecting electrodes form atransmission line, which involves a neglectable dispersion of the phasevelocities.

It is a further object of this invention to provide a cathode ray tube,comprising an electron beam deflection apparatus, wherein the bandwidthof the frequencies which involve an adequate deflection is broader thanin the known cathode-ray tubes.

In accordance with the invention in a charged particle beam deflectionapparatus consisting of a system of two electrodes, one of which is ahelical winding of substantially flat conductive ribbon, having aflattened part parallel to the axis of the winding, the other electrodehas two parts, an inner part disposed within the helical winding and anouter part practically completely surrounding the helical winding. Thewalls of these parts facing the helical winding are coaxial with thehelical winding and have cross-sections of a form similar to the form ofthe crosssection of the helical winding.

In this charged particle beam apparatus the dispersion of the phasevelocities is highly reduced, the second electrode being so constructedand positioned as to substantially prevent the lines of force of theelectrical field closing longitudinally. When either the inner part orthe outer part of the second electrode does not exist, as is the case inthe forementioned known apparatus, the lines of force of the electricalfield may easily close longitudinally and so one removes from the modeof propagation T.E.M.

Preferably the helical winding has, all over the winding, a constantdistance to the inner part and a constant distance to the outer part ofthe second electrode in order to have a characteristic impedance whichis constant along the circuit.

The distances between the helical winding and the two parts of thesecond electrode are preferably not longer than the pitch of the windingin order to assure a practically transversal closure of the lines offorce of the electrical field. Greater distance would not prevent assatisfactorily as possible the longitudinal closure of lines of force ofthe electrical field and so the deformation of signals by the dispersionof the phase velocities would not be prevented as satisfactorily aspossible.

The electrodes are preferably fixed together by means of a few thininsulating sheets so as to have a minimum of dielectric material betweenthe electrodes. As a matter of fact, the presence of dielectric materialincreases the dispersion changing locally the velocity of the wave.

The invention concerns particularly a cathode-ray tube, comprising anelectron gun for the production of an electron beam and comprising acharged particle beam deflection apparatus, as just described, for thedeflection of the electron beam, wherein according to the invention thepath of the electron beam extends in the space between the helicalwinding and the second electrode of said apparatus in the same generaldirection as the axis of the winding and along the flattened part of thewinding. In this cathode ray tube one has the advantages of thedescribed deflection apparatus, so that it involves the possibility oftransmitting signals with frequencies of a very broad band-width. Thecathode ray tube is so constructed that the beam extends along theflattened parts of the electrodes. These parts permit having a uniformtransverse electric field along them, where as the curved parts create aslight distortion of the field.

The invention will now be described with reference to the accompanyingdrawing, of which:

FIGURE 1 represents a longitudinal section of a charged particle beamdeflection apparatus;

FIGURE 2 represents a cross-section of a charged particle beamdeflection apparatus; and

FIGURE 3 represents on a large scale the helical winding of a chargedparticle beam deflection apparatus.

In the figures is shown a helical winding 5 of substantially flatconductive ribbon, which serves as one of the deflecting electrodes ofthe apparatus. The second electrode of the apparatus has two parts, aninner part 8 and an outer part 1. These parts are electricallyconnected, which is not shown in the drawing.

The outer part 1 is a block of metal, which has the form of aparallelopiped. It consists of two parts asseru 4 and the helicalwinding is so positioned within the tunnel that all the points of theexterior surface of the winding have the same distance to the wall ofthe tunnel. The inner part 8 of the second electrode is a flat ribbon ofmetal. Its cross-section resembles the cross-section of the tunnel 4 andit is so positioned within the helical winding 5, that all the points ofthe interior surface of the winding have the same distance to it. Thehelical winding 5 and the inner part 8 of the second electrode aremaintained in position within the tunnel 4 by means of three thin sheetsof mica 6. Two of these sheets are disposed between the helical winding5 and the wall of the tunnel 4. They are fixed in the notches '7 in thewall of the tunnel 4. The third one is disposed between the helicalwinding 5 and the inner part 8 of the second electrode. The twoextremities of the helical winding 5 are connected to coaxial plugs 9 bymeans of which the voltage signals may be applied to the transmissionline and the circuit may be closed by its characteristic impedance. Thedistance between the helical winding 5 and the inner part 8 of thesecond electrode is 1.2 mm. and the distance between the helical winding5 and the outer part 1 of the second electrode is 1.8 mm. The pitch ofthe helical winding is 2.8 mm. This results in a characteristicimpedance of ohms and a practically negligible dispersion of the phasevelocities. The reference It) in FIG. 2 refers to a preferred positionof the path of the charged particle beam. In this position the path ofthe charged particle beam extends between the flattened parts of theelectrodes and from this position the mica sheets cannot be seen. Apractically equally favorable position exists just opposite to this oneon the other side of the helical winding between the helical winding andthe inner part 8 of the second electrode. In cathode ray tubes accordingto the invention comprising an embodiment of the deflection apparatus,as just described, the electron gun and the deflection apparatus are sopositioned in the cathode ray tube, that the electron beam path has oneof these preferred positions in the deflection apparatus. The electrodesof the deflection apparatus in these tubes are preferably gilt toprevent oxidation during the finishing of the tubes.

What is claimed is:

1. A cathode ray tube comprising a source of electrons, means forprojecting an electron beam from said source between the electrodes of abeam deflection apparatus, said apparatus consisting of a system of twoelectrodes, one of which is a helical winding of substantially flatconductive ribbon having a flattened part parallel to the axis of thewinding, the other electrode comprising an inner flat part disposedwithin and extending along the axis of the helical winding and parallelto said flattened part, and an outer part practically completelysurrounding the helical winding the walls of which parts facing thehelical winding are coaxial with the helical winding and havecross-sections of a form similar to the form of the crosssection of thehelical winding.

2. A cathode ray tube, as claimed in claim 1, characterized in that thehelical winding has all over the winding a constant distance to theinner part and a constant distance to the outer part of the secondelectrode.

3. A cahode ray tube, as claimed in claim 2, characterized in that thedistances between the helical winding and the two parts of the secondelectrodes are not longer than the pitch of the winding.

4. A cathode ray tube, as claimed in claim 3, characterized in that theelectrodes are fixed together by means of a few thin insulating sheets.

5. A cathode ray tube as claimed in claim 1, characterized in that thepath of the electron beam extends in the space between the helicalwinding and the second electrode of said apparatus, in the same generaldirection as the axis of the winding and along the flattened part of thewinding.

References Cited UNITED STATES PATENTS ROBERT SEGAL, Primary Examiner.

